Technical Abstract: Production system, diet, geographic location, and climate affect the environmental footprint of dairy farms. The objective of this analysis was to estimate ammonia emissions and carbon and energy footprints of dairy farms in the Northeastern United States (US) and Northern Europe (NE). Sixteen US farms [average size 121 ha (SD = 19.7, with min = 16 and max = 304 ha)] and 11 farms located in NE [93 ha (SD = 44.8, with min = 26 and max = 201 ha)] were included in the analysis. Parameters were established to simulate all farms with the Dairy Gas Emission Model (DairyGEM). Important input data for each farm were the number of animals including replacement heifers, milk production and milk composition, feeds (forages and concentrates) fed and their nutrient contents, pasture use, crude protein concentration of the diets, housing type, and manure handling practices. Output data were analyzed using the MIXED procedure of SAS with farm as a random effect. Estimated ammonia emissions ranged from 5.1 to 13.6 g ammonia/kg fat and protein-corrected milk (FPCM) with the emissions on NE farms averaging 36% less (P < 0.001) than the US farms (Table 1). Carbon footprints ranged from 0.77 to 1.47 kg CO2e/kg FPCM with the NE farms averaging 17% greater than the US farms. Energy use ranged from 2.45 to 3.81 MJ/kg FPCM with the NE farms averaging 19% greater than the US farms. The lower ammonia emissions for NE were attributed to cooler temperatures, lower dietary protein content, and faster incorporation of manure when applied to fields. Greater carbon and energy footprints of the NE farms were primarily due to an average 16% lower milk production per cow compared with the US farms.